Particularly text files.

What's the point of being able to upload a CSS file if I can't edit the CSS file?

Uploading a new updated CSS file with the same name doesn't replace it, it creates a duplicate file with an entirely new URL.

This makes managing stylesheets laborious and untenable.

Overall there really needs to be a better way to manage stylesheets across the platform, but at least being able to edit an uploaded CSS file in the Media Library would be a good start.